Online Monitoring of Power Cables Tangent Delta Based on Low-Frequency Signal Injection Method

To improve the reliability of power systems, online cable condition monitoring must be implemented to replace traditional regular power outage maintenance. Existing online monitoring methods have certain limitations. In this article, a novel method based on low-frequency signal injection is proposed to monitor power cable insulation conditions online. For this method, a low-frequency signal is injected into the power system via the potential transformer (PT) open delta configuration. The cable conductor voltage and leakage current are detected. The interpolating windowed fast Fourier transform (FFT) algorithm is applied to calculate the dielectric loss angle. Then, the cable tangent delta (tan delta) can be deduced, and the cable condition can be assessed. A distribution network system is built based on the power system computer-aided design (PSCAD) software. The frequency and amplitude of the injected signal are simulated and discussed. An online monitoring platform is established in the laboratory. Thermal-aged cable samples and water tree-aged cable samples are prepared and measured. The experimental results confirm that the proposed method can effectively assess power cable insulation.